Graphing Lines Normal to Best Fit Line Based on Max and Min Y

**castabya** · 03-19-2010, 10:50 AM

In a scatter plot, I am graphing the results of taking 2 measures of the same part twice (column 1 is measure 1 and plotted as X, column 2 is the same part measured again, and is plotted as Y). I have added a trend line and include the equation of the line and the R squared value. Everything looks good, but what I do not know is:

1) How do I add a 45 degree line to a scatter plot in addition to the trendline?

2) How do I throw out the farthest Y value from the best fit line, and then graph a line parralel to the best fit line +/- that distance from the best fit line?

3) As I change the data entered into the chart, how do I force the scale to ALWAYS foce X and Y scales to be the same?

Thanks in advance for any help you can provide on this.

**shg** · 03-19-2010, 11:20 AM

1. Add another series plotted from two points.

2. You need a way to exclude the outlier via formula or other means, and then duplicate the data for plot, replacing the outlier with #N/A.

3. Choose the points in 1. so they exceed the range of x and y values in the main data.

**castabya** · 03-20-2010, 09:13 AM

That worked. To be honest, I am so green on Excel, that I had to look up your solution of adding other series, and how to make that work. However, I found an example on the forum with an included spread sheet that clued me in. Once I tried that, my sheet does just what I wanted it to. Thanks for the help.